A typical Electronic Article Surveillance and Inventory Control (“EASIC”) system in a retail setting may comprise a monitoring system and at least one control tag or label attached to an article to be protected from unauthorized removal. The monitoring system establishes a surveillance zone in which the presence of control tags and/or labels can be detected. The surveillance zone is usually established at an access point for the controlled area (e.g., adjacent to a retail store entrance and/or exit). If an article enters the surveillance zone with an active control tag and/or label, then an alarm may be triggered to indicate possible unauthorized removal thereof from the controlled area. In contrast, if an article is authorized for removal from the controlled area, then the control tag and/or label thereof can be deactivated and/or detached therefrom. Consequently, the article can be carried through the surveillance zone without being detected by the monitoring system and/or without triggering the alarm.
In some scenarios, it is desirable to track control tags present within the controlled area. As such, various solutions have been derived for this purpose. One such solution involves discovering Radio Frequency Identification (“RFID”) enabled control tags using an RFID interrogator. The RFID protocols employed by this solution work well for a small number of control tags in a physically controlled environment. However, in environments with a relatively large number of visible and/or moving control tags, there are severe limitations in tracking items and detecting theft in a crowded retail facility.
Since thousands of tagged products may enter and exit a particular retail facility every day, there are challenges to determine the locations of all the control tags. This is particularly problematic for continuously tracking the control tags. Monitoring at the store exits needs to accurately and quickly track control tags that are exiting the retail store while ignoring hundreds or more stationary control tags. With the current RFID protocols and the exit constraints, the exit monitoring process misses control tags and fails to detect theft of retail items. Also, RF reflections from the surrounding environment often cause false positive detections.
The RFID protocol problem results from the number of control tags detected or “seen” by the RFID interrogator and the ability to track single control tags quickly. Typically, the RFID protocol opens up a variable number of timeslots and all the control tags are randomly assigned to the timeslots for communication. Too many timeslots wastes a lot of valuable time, and too few timeslots cause many collisions (e.g., more than 1 control tag per timeslot) such that there are reduced communications. Store environments with many control tags and reflections of control tags results in a large amount of time in communication with unimportant control tags. This wasted time prevents the accurate tracking of control tags at the retail store exits.
Many techniques that can be used to track control tags (such as phase changes or Doppler effects) don't work well in environments of more than a few visible control tags or when a control tag is only seen for less than a second. Many of these techniques require at least five samples to accurately determine control tag position and motion. In the limited confines of a retail store environment, there is generally not enough time and samples to effectively use these techniques with sufficient accuracy. Another method has attempted to define an exclusion zone which uses a large area of physical isolation to greatly reduce the number of control tags seen and reflections by other control tags. This method works technically, but wastes a great deal of retail store space that is either not available or expensive. Control tag session control which is a method of grouping control tags and isolating groups of control tags from each other such that control tags of each group can only work in particular area or zone of the retail store environment. In this case, the retail stores often require multiple RFID interrogators to cover multiple physical zones of the retail store environment. As such, the effectiveness of session control drops off rapidly in most store environments.
There are collisions with multiple RFID interrogators trying to control various session parameters at the same time causing many control tags to be missed. In addition, control tags can move out of its assigned zone without being detected. There have been RFID devices which combine acceleration shock detection devices and RFID devices. In this case, the RFID device of the control tag is read to determine if a product attached thereto has experienced a shock of at least 50 g. Despite the advantages of this solution, it doesn't solve the problem of quickly communicating (“talking”) to the correct control tags in a retail store environment.